The invention relates to microfluidic devices, and in particular, to a rotary microfluidic valve.
The last few years have seen a great increase in the use of microfluidic chips for analytical chemistry. Microfluidic chips are generally constructed using planer micromachining techniques. In particular, the chips are built by stacking layers of materials and by etching portions of these layers away or by building upon them with further layers. The most basic microfluidic chip is a closed channel built by etching a trench into a first substrate and by bonding another substrate over these trenches. Access holes (vias) may be drilled in either the first or second substrates prior to bonding to provide a connection between the outside world and the internal channels.
The are many advantages of chip-based systems for analytical chemistry. First, a high degree of integration is attainable as entire networks of channels can be built into a chip. For example, chromatographic sample preparation, metering, injection and separation, previously carried using discrete components connected together with tubing, can occur in a single device. Second, this integration dramatically reduces the total volume of the system, reducing reagent costs and reducing resolution losses due to the high volume of connections. Third, as diffusion time is proportional to the square of the diffusion distance, the small channel dimensions attainable using microfluidics allow vast reductions in thermal and molecular diffusion times and thereby allow faster reactions. In general, microfluidic devices allow a reduction in the cost of materials and in reaction time while improving detection efficiency.
However, macromachined rotary valves are still widely used, especially in the fields of liquid chromatography (LC) and High Performance Liquid Chromatography (HPLC), where such valves are standard for controlling injection volumes, dilution rates and for defining a flow path. The advantages of transferring chemical analysis to a microfludic chip platform is hindered by a loss of functionality provided by conventional components, such as the macromachined rotary valves.
U.S. Pat. No. 4,625,569 discloses a macromachined rotary valve having a number of rotor and stator combinations. As detection techniques improve, the LC and HPLC systems are moving towards smaller and smaller volumes. Accordingly, discrete tubing connecting to the valve and the size of conventionally machined conduits, as disclosed in U.S. Pat. No. 4,625,569, are disadvantageous, as they become a significant contributor to the overall volume.
U.S. Pat. No. 6,267,143 discloses a ferrule cluster to reduce the valve volume, producing a 54 nL port-to-port valve. The assignee of this patent (Upchurch Scientific) has applied for a U.S. patent for a 25 nL rotary valve that in addition to the ferrule cluster uses a micromachined rotor. As such, this valve is a hybrid between conventional machining techniques and discrete fluid transfer conduits and micromachined techniques and integrated conduits. The valve disclosed in U.S. Pat. No. 6,127,143 is disadvantageous, as it discloses a conventional macromachined stator, requiring discrete tubing and contributing significantly to the overall volume of the system.
There are several microfluidic valves known in the prior art. One of these is the family of diaphragm valves. Such valves use a thin layer of an elastic material, the diaphragm, as one of the layers in the microfluidic chip. Channels connect to either side of a valve cavity, which is interrupted by the diaphragm. In the closed state the diaphragm pushes against a valve seat preventing fluid from flowing past the seat. In the open state the diaphragm is released from the valve seat allowing fluid to flow between the channels. Such a valve has several disadvantages. The first is that as additional diverse materials and layers are used processing becomes more complicated, more prone to failure and thus more expensive. A second is that few materials are suitable for use as a membrane. The most popular membrane material is silicone rubber which is quite permeable to a wide range of commonly used liquids and gasses. A thin silicon substrate is another widely used choice that has better chemical, physical and process compatibility than silicone but which is rather rigid in comparison.
The majority of the prior art diaphragm valves have limited functionality. They are 1:1 or 1:2 valves. Valving schemes (such as many used widely in liquid chromatography) that require 1:n valves require n individual 1:1 valves or nxe2x88x921 individual 1:2 valves. As the number of such valves on a single chip increases, the cost of the composite valve also rises as the process yield necessarily goes down. In addition, each constituent valve has its own dead volume and swept volume. The total dead and swept volume of the 1:n valve becomes large very quickly.
The known microfluidic valves are also limited in terms of sustainable pressure. Sustainable pressures of 5-8 psi are typical, though sustainable pressures of up to 140 psi have been reported.
Further, diaphragm valves raise the complexity and the price of a microfluidic chip. A large potential market for microfluidics is in settings (e.g. medical diagnostics, drug discovery) where cleanliness and ease-of-use necessitates the one-time use of microfluidic chips. Therefore, a valve which features the low volumes associated with microfluidics but which simplifies manufacturing is desirable.
Accordingly, a need exists for a microfluidic valve that is easily manufactured, highly flexible in functionality, and that can operate at higher pressures than prior art valves. It is also seen that there is a need for rotary valve that has advantages over the current state-of-the-art in macromachined rotor valves in nanoliter swept volumes and in the integration with microfluidic pathways instead of discrete capillary or tubing.
According to a first aspect of the present invention, a microfluidic valve is provided. The valve comprises:
a) a stator chip defining at least one inlet and at least one outlet therein; and
b) a rotor sealably engaging the stator chip, the rotor defining at least one rotor channel therein, said rotor being rotatable between a closed position preventing fluid communication between at least one inlet and at least one outlet, and an open position where at least one rotor channel is in fluid communication with at least one inlet and at least one outlet.
Preferably, the rotor has a facing surface and the stator chip defines a stator cluster portion for sealably engaging the facing surface of the rotor, wherein the at least one inlet and the at least one outlet open onto the stator cluster portion, and, the stator chip includes at least one microfluidic device in fluid communication with the stator cluster portion.
According to a second aspect of the invention, a microfluidic valve is provided. The valve comprises:
a) a stator chip defining an inlet and an outlet therein; and
b) a second chip sealably engaging the stator chip, the second chip defining a valve channel therein, the second chip being movable between a closed position preventing fluid communication between the inlet and the outlet, and an open position where the valve channel is in fluid communication with the inlet and the outlet.
Preferably, the second chip defines a facing surface and the stator chip defines a stator cluster portion for sealably engaging the facing surface of the second chip, wherein the inlet and outlet open onto the stator cluster portion, and the stator chip includes at least one microfluidic device in fluid communication with the stator cluster portion.
According to a third aspect of the present invention, a stator chip for a microfluidic rotary valve having a rotor is provided. The stator chip comprises:
a) a first planar substrate having a contact face; and
b) a second planar substrate having a contact face sealably secured to the contact face of the first planar substrate;
wherein the first planar substrate defines a first portion of each of at least one inlet and at least one outlet, and the second planar substrate defines a second portion of each of the at least one inlet and the at least one outlet, the at least one inlet and the at least one outlet being adapted to be brought into fluid communication by the rotor.
Preferably, the stator chip defines a stator cluster portion for sealably engaging a facing surface the rotor, wherein the at least one inlet and the at least one outlet open onto the stator cluster portion, and wherein the stator includes at least one microfluidic device.
According to a fourth aspect of the present invention, a method of manufacturing a stator chip for a microfluidic rotary valve is provided. The method comprises the steps of:
a) forming at least one first inlet channel and at least one first outlet channel in a first planar stator substrate;
b) forming at least one second inlet channel and at least one second outlet channel in a second planar stator substrate;
c) sealably securing the first stator substrate to the second stator substrate, such that the at least one first inlet channel is in fluid communication with the at least one second inlet channel and the at least one first outlet channel is in fluid communication with the at least one second outlet channel.
According to a fifth aspect of the present invention, a method of manufacturing a planar rotor chip for a microfluidic rotary valve is provided. The method comprises the steps of:
a) forming a rotor contact surface on the rotor chip;
b) forming a rotor channel in the rotor contact surface, the rotor channel being adapted to bring at least one stator inlet channel in fluid communication with at least one stator outlet channel; and
c) forming a low friction material layer on the contact rotor surface.